Selective oxidation of CO with modified Pd/ZnO catalysts in the presence of H2: Effects of additives and preparation variables
Selective oxidation of CO with modified Pd/ZnO catalysts in the presence of H2: Effects of additives and preparation variables
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DOI：
10.1016/j.apcatb.2007.10.001
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发表时间：
2008-02
影响因子：
22.1
通讯作者：
N. Iwasa;S. Arai;M. Arai
中科院分区：
文献类型：
--
作者：
N. Iwasa;S. Arai;M. Arai
以各种载体材料（ZnO、Ga 2 O3、SiO2、CeO 2、In 2 O3和Al 2 O3）为载体的负载型Pd催化剂对于用O2选择性氧化富H2气体中的CO表现出较差的活性和选择性。最活跃的催化剂是Pd/ZnO中的六个样品检查。该催化剂中的Pd物种以PdZn合金的形式存在，与其它催化剂中的金属Pd物种相比，该合金对反应更有效。Pd/ZnO催化剂的活性可以通过添加碱性化合物，特别是Cs和Rb而显著提高。这些添加剂被证明可以增强CO氧化，但抑制不希望的H2氧化。采用优化的Cs改性Pd/ZnO催化剂（Cs/Pd=3），在433 K下，CO/O2/H2/CO2（0.5/2.0/23/7.0）混合气体的CO浓度可降至40 ppm，而H2转化率控制在<10%。程序升温脱附实验表明，Cs的加入影响了Pd/ZnO催化剂中Pd Zn合金颗粒对CO和H2的吸附/脱附行为，但对Pd Zn合金晶粒的大小没有影响。在CO和H2同时存在的条件下，Cs助剂的加入减弱了CO在催化剂上的吸附强度，增加了与CO和H2弱相互作用的H2的量，从而提高了Cs改性Pd/ZnO催化剂的CO选择氧化活性。
Supported Pd catalysts on various support materials, ZnO, Ga2O3, SiO2, CeO2, In2O3, and Al2O3, exhibit poor activity and selectivity for the selective oxidation of CO in H2-rich gas with O2. The most active catalyst is Pd/ZnO among the six samples examined. The Pd species exist in the form of PdZn alloy in this catalyst and the alloy is more effective for the reaction compared with metallic Pd species of the other catalysts. The activity of Pd/ZnO catalyst can be significantly improved by the addition of alkali compounds, in particular Cs and Rb. These additives were shown to enhance the CO oxidation but suppress the undesired H2oxidation. With the optimized Cs-modified Pd/ZnO catalyst (Cs/Pd=3), the CO concentration of a mixture of CO/O2/H2/CO2(0.5/2.0/23/7.0) can be reduced to a 40ppm level at 433K, while controlling the H2conversion level to <10%. Temperature programmed desorption measurements indicate that the addition of Cs affects the adsorption/desorption behavior of CO and H2on PdZn alloy particles in the Pd/ZnO catalyst but not the size of PdZn alloy crystallites. The Cs promoter is effective to weaken the strength of CO adsorption on the catalyst and increase the amount of H2weakly interacting with them in the presence of both CO and H2, resulting in the enhanced selective CO oxidation activity of the Cs-modified Pd/ZnO catalyst.